This invention relates to a drilling device for a rock drill with a rotary drive for the drill steel and a percussion mechanism.
A hydraulic rock drill is known through U.S. Pat. No. 4,064,950 in which the control valves for percussion power and rotation speed are located in the control panel apart from the rock drill itself. Furthermore, the percussion apparatus and the rotation motor have separate hydraulic circuits. The maximum percussion power is adjusted by a pressure relief valve in the hydraulic circuit of the percussion mechanism and the maximum rotation power is adjusted by a pressure relief valve in the hydraulic circuit of the percussion mechanism.
With such drilling devices it sometimes happens that the drill steel gets jammed and cannot be rotated further. When under such conditions the percussion mechanism continues to strike the drill steel, it can happen that the latter is driven into the rock and cannot be retracted any more.
In the German Offenlegungsschrift No. 34 39 268 a similar drilling device has been proposed where the percussion mechanism and the hydraulic motor are arranged in series. This device does not have the drawback mentioned above: When the hydraulic fluid cannot flow through the motor because the motor is stopped by the drill then no flow passes through the percussion mechanism. Therefore, percussion stops when the drill rod gets jammed. However, this prior art device has other drawbacks: The sum of the power output of the hydraulic motor and the percussion mechanism is constant but the power distribution between the two is indetermined.
In Swiss Patent No. 559 088 it was proposed to directly couple the percussion frequency with the rotation rate of the motor. However, with this proposal it is not possible to operate the percussion mechanism and the motor independently.